This invention relates to a valve member in a two-stage servo assembly that controls the operation of an output motor in response to an input force.
Two-stage servo valve systems have been used to provide fluid to an output device such as a piston, where the piston movement controls the operation of a motor. Such a two-stage servo valve is disclosed in U.S. Pat. No. 3,745,883 which has a first spool valve connected to a second spool valve. The first spool is connected to an input member and the second spool is connected to the piston. The first spool moves in response to the input member and allows pressurized fluid to flow to the second spool valve. The pressurized fluid acts on the second spool valve and overcomes the force of a centering spring to thereafter allow pressurized fluid to move the piston. Movement of the piston provides an operational force for operating flaps, elevators, bleed valves, etc. on an aircraft. Unfortunately, the spool valves in such two-stage devices often times stick due to differences in expansional characteristics with the housing caused by temperature changes. Thus, for a smooth operating valve, the pressurized fluid must be maintained at a substantially constant temperature level.
The sticking problem could be avoided through the use of floating discs such as disclosed in U.S. Pat. No. 3,402,737. However, the response time in moving the first and second stage disc from a null position to an actuating position has not been acceptable for most devices in aircraft due to rapid changes in operating conditions.